Amazon has added a listing for a Refurbished Kindle DX for $399, a savings of $90 over the new units. These are in stock, at least for now, and come with the same 30 day, no questions asked, Amazon return policy, as well as the same one-year warranty that you get with any Kindle purchase.
As some readers have seen me mention before, we have one refurbished Kindle here (an original Kindle) and it was indistinguishable from a new Kindle when it arrived and has performed flawlessly (it just got back from a one month trip to the wilds of South Dakota). And I also have a Kindle DX, which I use (mostly) for PDF's that don't convert well (or I don't feel like converting), as well as a few books from Amazon that have maps or photos that just look better on the big screen.